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Review and Measurements of Little Labs Monotor Headphone Amp

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#61
My pleasure. I wonder if they think high-impedance headphones are more common in pro space and hence that design choice.
Historically when recording studios began employing headphones during tracking they would use a single power amp to drive many pairs, sometimes there were headphone "drop boxes" positioned throughout the studio area for the musicians. These were usually paralleled TRS jacks, though more "sophisticated" designs would include a potentiometer to allow individual attenuation control for the musicians. As you have probably already surmised these parallelled headphones would create a very low impedance load to the power amplifier, and a typical tracking session could use from 4 to 20 or more sets of headphones. For this reason headphones with much higher impedance were used, 600Ω is not uncommon.
 

JohnYang1997

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#62
Historically when recording studios began employing headphones during tracking they would use a single power amp to drive many pairs, sometimes there were headphone "drop boxes" positioned throughout the studio area for the musicians. These were usually paralleled TRS jacks, though more "sophisticated" designs would include a potentiometer to allow individual attenuation control for the musicians. As you have probably already surmised these parallelled headphones would create a very low impedance load to the power amplifier, and a typical tracking session could use from 4 to 20 or more sets of headphones. For this reason headphones with much higher impedance were used, 600Ω is not uncommon.
But by that logic, low impedance performance is going to be relevant. The original assumption would serve no purpose, right? At any rate, well engineered single 1622 amp will very likely to outperform this.
 
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#63
But by that logic, low impedance performance is going to be relevant. The original assumption would serve no purpose, right? At any rate, well engineered single 1622 amp will very likely to outperform this.
This particular headphone amp was probably designed as a personal use device, not intended to drive an entire session.
 
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#66
How much power is necessary for driving a headphone?
I am using daily both the HD600 Sennheiser 300 ohms and an Audeze LCD-X 20 ohms and both work wonderfully with the monotor, and certainly without distortion at very loud volume.
Those two phones are the two most popular used by professionals paired with the monotor.
I listen to all genres of music and not once did I notice distortion even at dangerously high volumes. Now I'm not familiar with the Hifiman HE-400i, but I'll take Amirm at his word that the monotor distorted before the HE-400i did.
But, and this is very important, the casual reader of this review would most likely overlook this. This HE-400i is a rare case, a new breed of headphone that is very low sensitivity, and also low impedance (FYI low impedance phones are typically very sensitive). I think another headphone with that spec is the Mr. Speaker Aeron (closed back), a headphone I like a lot. I have never pushed it so loud the monotor distorted, but I don't dispute that you can.

In my experience with headphone amps, voltage gain, which is necessary to drive phones to a respectable level, is far more important a spec than power output. Rarely is over 100mw of power necessary to happily drive a well-designed headphone. The Monotor has 13.8 dB of gain. I chose that gain for a perfect pairing with my most popular headphone the HD600. That gain on the HD600 gives you a great range from soft to ridiculously loud, and oh so clean... Now where that gain becomes a problem is with super sensitive phones, mostly IEMS. Some IEMS are crazy sensitive, those IEMs I do not recommend with the monotor.
The monotor is not a one size fits all, you don't use a Porsche for off-roading now, do you?
That being said I have some drummer friends that love it super loud and use the monotor on stage to power their IEMS, they couldn't be happier. I worry about their ear health.
Jonathan, I just found this thread, as I'm on the hunt for the best cue amps for both my studio & for my band's live cue system. I've already spent a small fortune, & not yet totally happy. VERY interested in the Monotor, but I have to admit, Amir's review really troubles me, despite your reply. Hoping for more thoughts from you, if you have the time:
-----------------------
Because of my dual use, my amps have to drive both 600 ohm Beyers and Shure SE846's, and sadly the Shures (which are amazing IEM's for singers) are only 9 ohms. Yes, I read your previous comments, of course, but my personal experience, with other headphone amps, is different: The O2 types fail miserably at 9 ohms. (though I LOVE their midrange presence.) The JDS Atom does quite well. The SP200 THX also fails to some extent, though that's also partially due to its badly conceived gain structure, I think. Still.... But the Atom isn't my dream amp, as it's somewhat lacking in bass and overall fullness, and has a slightly narrow soundstage. The THX is significantly better in both regards, but has issue with IEMs. It also has an oddly recessed upper midrange, despite measuring flat on lab equipment. From what I've been reading, that's typical of all the THX chips, and is not very good for singers.

So..... Is Amir just wrong? I can't help noting that no ads for the MONOTOR give output power specs, so one might assume... well, you know.

Let's say (just theoretically) someone buys one of your amps, loves the sound with 600 ohm cans, but disagrees with you re the IEMs. Sound is subjective, after all. Can anything be done? How about using "impedance converter" adapters? (which I assume are just L pads.) That's actually resistance, not impedance, but could that help? (Or hurt, since the resistance would also knock down the power transfer?)

How about beefing up the power supply for more current? (warrantee be damned...)

Or, again, do you feel that strongly that Amire got it wrong?

thx.
 

Noob

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#67
Jonathan, I just found this thread, as I'm on the hunt for the best cue amps for both my studio & for my band's live cue system. I've already spent a small fortune, & not yet totally happy. VERY interested in the Monotor, but I have to admit, Amir's review really troubles me, despite your reply. Hoping for more thoughts from you, if you have the time:
-----------------------
Because of my dual use, my amps have to drive both 600 ohm Beyers and Shure SE846's, and sadly the Shures (which are amazing IEM's for singers) are only 9 ohms. Yes, I read your previous comments, of course, but my personal experience, with other headphone amps, is different: The O2 types fail miserably at 9 ohms. (though I LOVE their midrange presence.) The JDS Atom does quite well. The SP200 THX also fails to some extent, though that's also partially due to its badly conceived gain structure, I think. Still.... But the Atom isn't my dream amp, as it's somewhat lacking in bass and overall fullness, and has a slightly narrow soundstage. The THX is significantly better in both regards, but has issue with IEMs. It also has an oddly recessed upper midrange, despite measuring flat on lab equipment. From what I've been reading, that's typical of all the THX chips, and is not very good for singers.

So..... Is Amir just wrong? I can't help noting that no ads for the MONOTOR give output power specs, so one might assume... well, you know.

Let's say (just theoretically) someone buys one of your amps, loves the sound with 600 ohm cans, but disagrees with you re the IEMs. Sound is subjective, after all. Can anything be done? How about using "impedance converter" adapters? (which I assume are just L pads.) That's actually resistance, not impedance, but could that help? (Or hurt, since the resistance would also knock down the power transfer?)

How about beefing up the power supply for more current? (warrantee be damned...)

Or, again, do you feel that strongly that Amire got it wrong?

thx.
Your issue seems to be that you require a very very small amount of power for very efficient in-ears, but you need that tiny bit of power to be very clean. The monotor is designed for headphones that actually need some juice. I would not recommend running very sensitive and low impedance IEMs through a powerful amp. Get something with a low gain setting and preferably a digital or relay attenuator to get good channel matching at low volumes. The Monotor would probably be more powerful and much higher of a gain than you would ever want for an SE846.

I’m really enjoying my Geshelli archel 2.5, but I don’t think I would recommend that for such a sensitive and low impedance in-ear. . . It’s actually a harder issue than it seems. I know many dac/amps that would do well in this situation like the topping dx3 pro or the famous RME ADI-2 DAC, but a pure amp that is suitable for extremely low impedance IEMs is rare. You should probably invest in an impedance adaptor. Then it would not matter so much. Just stick an adaptor into the Monotor, and you would be golden. Take it out for higher impedance cans, and the monotor could be your final solution.
 
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#68
I hear you, Noob, (thx) but unfortunately I need a cue amp that can handle both, all of the time.

I agree that "It’s actually a harder issue than it seems." There is clearly no perfect solution.

Hoping to hear from Jonathan on this.
 

Noob

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#71
Thx amps are definitely not considered noisy. The SP200 perhaps with extremely sensitive in-ears, but it is at too high of a gain anyway to be considered with such a sensitive in-ear. Getting a aaa789 or a aaa887 would work, but those are $400 a piece.
 

JohnYang1997

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#72
Thx amps are definitely not considered noisy. The SP200 perhaps with extremely sensitive in-ears, but it is at too high of a gain anyway to be considered with such a sensitive in-ear. Getting a aaa789 or a aaa887 would work, but those are $400 a piece.
I have designed amps that are 1/8th to 1/10th of noise of THX amps. 0.27uV vs 2-3.6uV
 

JohnYang1997

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#73
Thx amps are definitely not considered noisy. The SP200 perhaps with extremely sensitive in-ears, but it is at too high of a gain anyway to be considered with such a sensitive in-ear. Getting a aaa789 or a aaa887 would work, but those are $400 a piece.
But if you weren't talking about noise. What was the issue of powerful amps?
 

Noob

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#74
But if you weren't talking about noise. What was the issue of powerful amps?
Power. The SP 200 is a great example. The lowest gain setting is so high that you need to turn the potentiometer very far down for something like a SE846, and turning an analog potentiometer down that far could expose channel imbalance.

I’m not so concerned with the 789 and 887 amps because they have actually been tested by people with very sensitive in-ears on the lowest gain and found to have low enough noise for it to not be an issue, and the lowest gain is low enough that one would not need to turn the pot so low as to get noticeable channel imbalance.

This is theoretical as I have never used a pair of SE846s. Just reading that 114dB/mw sensitivity and 9 Ohm impedance is making me cautious you could blow out your ears by accident with something that sensitive on a powerful amp. Safety is a priority.
 

JohnYang1997

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#75
Power. The SP 200 is a great example. The lowest gain setting is so high that you need to turn the potentiometer very far down for something like a SE846, and turning an analog potentiometer down that far could expose channel imbalance.

I’m not so concerned with the 789 and 887 amps because they have actually been tested by people with very sensitive in-ears on the lowest gain and found to have low enough noise for it to not be an issue, and the lowest gain is low enough that one would not need to turn the pot so low as to get noticeable channel imbalance.

This is theoretical as I have never used a pair of SE846s. Just reading that 114dB/mw sensitivity and 9 Ohm impedance is making me cautious you could blow out your ears by accident with something that sensitive on a powerful amp. Safety is a priority.
There's difference between power and gain. That's basic. SP200 is 6dB gain inherently, from differential amplifier. When you use balanced in you get 12dB gain in total just in low gain.
Yes, a well designed amplifier can have very low gain setting(-9dB on A90) yet still extremely powerful.
In terms of noise, sp200 is 3.6uV, 789 is 1.6uV, 887 seems to be a little lower and HPA4 is 2uV. RME ADI2 DAC seems to be around 0.6uV and A90 is only 0.27uV with 50mV SNR of 105dB. You can have extremely low noise and power at the same time.
An amp that has high gain doesn't mean it's powerful. An amp that has high power doesn't mean it has to be noisy.
 
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#76
I have a unit on order and looking forward to hearing it. i think the designer made some very valid points on his design choices. His ultimate design goal was for transparency, and every component, circuit, and lack there of was dedicated to achieving that. Makes sence to me. Adding things that will spec nice, but detract from it sonically (sans under extremes) went against his design philosophy. Sound choice, pardon the pun.

Specs are 1/2 truths. I'm glad he said 2 circuits can spec identically, but can sound very different based on their competent choices. The designers that make the best sounding gear know this. The human ear is remarkably sensitive, and we hear things in music, and there 'are' things' in music, and on recordings, and that probably can't be measured and graphed when evaluating gear. Musical timbre, air, realistic weight and body to instruments. Tube gear, may not always measure as well in many areas as solid state, but can be more musical, and realistic sounding, because they can capture certain things better regardless, based on their design. I've demoed plenty of audio devices (speakers, dacs, preamps..etc...) based on their exemplary measurements from glowing reviews, only to find that while they may be clean and detailed, they sounded 2d and clinical to me. Something was missed, and overlooked in their design, as their creators were chasing after specs. Audio design is an art form. Art is the marriage of science and emotion/intuition. It's important to design gear based on what sounds good, not just measuremnts.
 

hellboundlex

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#77
Audio design is an art form.
I read the thread with interest, because of the response of the designer.

What shocked me is that he didn't talk about the multiple outputs, the mixing buttons, and all the little things that make this a good studio device.

It's optimized with 300 ohm headphones in mind, which is fine for it's target audience. It also outperforms most of it's real competition.

What frustrated me also was the fact that the designer didn't take more pride in these measurements, and instead focused on the flaws. This is a product to be proud of, and this review is something he should be proud of as well.

I don't buy the whole objectivist vs. subjectivist arguments. Once we get past what is easy to hear, we have to rely on measurements. In this product, that's ok, because it measures great.
 
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#78
I read the thread with interest, because of the response of the designer.

What shocked me is that he didn't talk about the multiple outputs, the mixing buttons, and all the little things that make this a good studio device.

It's optimized with 300 ohm headphones in mind, which is fine for it's target audience. It also outperforms most of it's real competition.

What frustrated me also was the fact that the designer didn't take more pride in these measurements, and instead focused on the flaws. This is a product to be proud of, and this review is something he should be proud of as well.

I don't buy the whole objectivist vs. subjectivist arguments. Once we get past what is easy to hear, we have to rely on measurements. In this product, that's ok, because it measures great.
I guess he felt pressed to address the specific criticisms of the review, and I felt he did just that. My point is that being too measurement-centric in evaluating an audio device is flawed.. Measurements have a place indeed, but use your ears ultimately, with careful, thorough listening tests. One's ears are the ultimate measuring device. I trust mine.
 
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#79
I have been moding a few amps i have in hand, mainly in psu section. I am surprised that everything sound so similar after modification, even when they have different topology/opamps etc.

The designer is completely correct that one can make a dozen different circuits and make them sound the same. Not doubt that can be a good amp, but do one need the same sound from everything?
Sir, I think you misunderstood what Mr. Little was saying, and what I was saying. He was making the point that you could make 2 circuits that 'spec' the same, but they will 'sound' different, cause of the sonic attributes some of the different individual parts used in each. For sure, different capacitors, and resisters for example may have the same values, but sound completely different. This is how upgrades are done, or part of the experimental stages when doing R+D for a new product and getting the sound you are looking for - part selection. Again the point: specs, and measurements are useful, but only to a point.
 
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#80
I see what you are saying.. Valid enough, but kind of a side point to what was actually being discussed on the previous posts. The pieces discussed were being held accountable to specific measurements by the reviewer, and the designer explained why he made certain design choices. He explained that he could have changed, or added things to the circuit to improve on those measurements, but that the diffence in those measurement disparities are inaudible, but the circuit changes needed to reach them would have degraded the sonic performance of the unit, as he is following a less is more, straight wire with gain philosophy.

He's been designing for 40 years, and knows what he's doing. He knows what he's after. The unit is praised for its natural, transparent sound. So again, using only measurement goals as the holy grail in circuit design has its shortcomings. Listening is equally important.

I read a review here on the Benchmark DAC3, which was praised for its measurements. When you talk to the peopl att Benchmark, all they talk about are measurements, and specs. That was he entire design approach apparently. It was a remarkably clean and detailed Dac, but the least musical of the ones I auditioned.
 
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